Radiation-sensitive silver halide photographic emulsions containing silver chloride are known to offer specific advantages. For example, silver chloride exhibits less native sensitivity to the visible portion of the spectrum than other photographically useful silver halides. Further, silver chloride is more soluble than other photographically useful silver halides, thereby permitting development and fixing to be achieved in shorter times. Silver chlorobromide emulsions have found particular utility in applications requiring high contrast, such as graphic arts, and in applications requiring rapid processing, such as black-and-white and color print products.
A great variety of grain shapes have been observed in silver halide photographic emulsions. Although a variety of factors, such as the presence of grain growth modifiers or ripening agents or the choice of double- or single-jet precipitation, can have a substantial impact on crystal configuration, no one factor is of more importance than the halide present during grain precipitation.
It is well recognized in the art that silver chloride strongly favors the formation of crystals having {100} crystal faces. In the overwhelming majority of photographic emulsions silver chloride crystals when present are in the form of cubic grains. With some difficulty is has been possible to modify the crystal habit of silver chloride. Claes et al, "Crystal Habit Modification of AgCl by Impurities Determining the Solvation", The Journal of Photographic Science, Vol. 21, pp. 39-50, 1973, teaches the formation of silver chloride crystals with {110} and {111} faces through the use of various grain growth modifiers. Wyrsch, "Sulfur Sensitization of Monosized Silver Chloride Emulsions with {111}, {110} and {100} Crystal Habit", Paper III-13, International Congress of Photographic Science, pp. 122-124, 1978, discloses a triple-jet precipitation process in which silver chloride is precipitated in the presence of ammonia and small amounts of divalent cadmium ions. In the presence of cadmium ions control of pAg and pH resulted in the formation of rhombododecahedral {110}, octahedral {111}, and cubic {100} crystal habits.
Tabular silver bromide grains have been extensively studied, often in macro-sizes having no photographic utility. Tabular grains are herein defined as those having two substantially parallel crystal faces, each of which is substantially larger than any other single crystal face of the grain. The term "substantially parallel" as used herein is intended to include surfaces that appear parallel on direct or indirect visual inspection at 10,000 times magnification. The aspect ratio--that is, the ratio of diameter to thickness--of tabular grains is substantially greater than 1:1. High aspect ratio tabular grain silver bromide emulsions were reported by de Cugnac and Chateau, "Evolution of the Morphology of Silver Bromide Crystals During Physical Ripening", Science et Industries Photographiques, Vol. 33, No. 2 (1962), pp. 121-125.
From 1937 until the 1950's the Eastman Kodak Company sold a Duplitized.RTM. radiographic film product under the name No-Screen X-Ray Code 5133. The product contained as coatings on opposite major faces of a film support sulfur sensitized silver bromide emulsions. Since the emulsions were intended to be exposed by X-radiation, they were not spectrally sensitized. The tabular grains had an average aspect ratio in the range of from about 5 to 7:1. The tabular grains accounted for greater than 50% of the projected area while nontabular grains accounted for greater than 25% of the projected area. The emulsion having the highest average aspect ratio, chosen from several remakes, had an average tabular grain diameter of 2.5 microns, an average tabular grain thickness of 0.36 micron, and an average aspect ratio of 7:1. In other remakes the emulsions contained thicker, smaller diameter tabular grains which were of lower average aspect ratio.
Although tabular grain silver bromoiodide emulsions are known in the art, the presence of iodide is known to restrict aspect ratios. A discussion of tabular silver bromoiodide grains appears in Duffin, Photographic Emulsion Chemistry, Focal Press, 1966, pp. 66-72, and Trivelli and Smith, "The Effect of Silver Bromo-Iodide Precipitation Series", The Photographic Journal, Vol. LXXX, July 1940, pp. 285-288. Trivelli and Smith observed a pronounced reduction in both grain size and aspect ratio with the introduction of iodide. Gutoff, "Nucleation and Growth Rates During the Precipitation of Silver Halide Photographic Emulsions", Photographic Sciences and Engineering, Vol. 14, No. 4, July-August 1970, pp. 248-257, reports preparing silver bromide and silver bromoiodide emulsions of the type prepared by single-jet precipitations using a continuous precipitation apparatus.
Bogg, Lewis, and Maternaghan have recently published procedures for preparing emulsions in which a major proportion of the silver halide is present in the form of tabular grains. Bogg U.S. Pat. No. 4,063,951 teaches forming silver halide crystals of tabular habit bounded by {100} cubic faces and having an aspect ratio (based on edge length) of from 1.5 to 7:1. The tabular grains exhibit square and rectangular major surfaces characteristic of {100} crystal faces. Lewis U.S. Pat. No. 4,067,739 teaches the preparation of silver halide emulsions wherein most of the crystals are of the twinned octahedral type by forming seed crystals, causing the seed crystals to increase in size by Ostwald ripening in the presence of a silver halide solvent, and completing grain growth without renucleation or Ostwald ripening while controlling pBr (the negative logarithm of bromide ion concentration). Maternaghan U.S. Pat. No. 4,150,994, 4,184,877, and 4,184,878, U.K. Pat. No. 1,570,581, and German OLS publications 2,905,655 and 2,921,077 teach the formation of silver halide grains of flat twinned octahedral configuration by employing seed crystals which are at least 90 mole percent iodide. (Except as otherwise indicated, all references to halide percentages are based on silver present in the corresponding emulsion, grain, or grain region being discussed; e.g., a grain consisting of silver chlorobromide containing 60 mole percent bromide also contains 40 mole percent chloride.) Lewis and Maternaghan report increased covering power. Maternaghan states that the emulsions are useful in camera films, both black-and-white and color. Bogg specifically reports an upper limit on aspect ratios to 7:1, and, from the very low aspect ratios obtained by the examples, the 7:1 aspect ratio appears unrealistically high. It appears from repeating examples and viewing the photomicrographs published that the aspect ratios realized by Lewis and Maternaghan were less than 5:1. Although Bogg, Lewis, and Maternaghan refer to the preparation of tabular silver halide emulsions broadly, they provide no specific examples or teachings directed to the preparation of tabular silver chlorobromide emulsions.
Japanese patent application publication 142,329, published Nov. 6, 1980, appears to be essentially cumulative with Maternaghan, but is not restricted to the use of silver iodide seed grains. Further, this publication specifically refers to the formation of tabular silver chlorobromide grains containing less than 50 mole percent chloride. No specific example of such an emulsion is provided, but from an examination of the information provided, it appears that this publication obtained a relatively low proportion of tabular silver halide grains and that the tabular grains obtained are of no higher aspect ratios than those of Maternaghan.
Wey, U.S. Ser. No. 429,403, filed concurrently herewith and commonly assigned, titled IMPROVED DOUBLE-JET PRECIPITATION PROCESSES AND PRODUCTS THEREOF, which is a continuation-in-part of U.S. Ser. No. 320,908, filed Nov. 12, 1981, now abandoned discloses a process of preparing tabular silver chloride grains which are substantially internally free of both silver bromide and silver iodide. The emulsions have an average aspect ratio of greater than 8:1.
Maskasky U.S. Ser. No. 431,455, filed concurrently herewith and commonly assigned, titled SILVER CHLORIDE EMULSIONS OF MODIFIED CRYSTAL HABIT AND PROCESSES FOR THEIR PREPARATION, which is a continuation-in-part of U.S. Ser. No. 320,898, filed Nov. 12, 1981, now abandoned, discloses a process of preparing tabular grains having opposed major crystal faces lying in {111} crystal planes and, in one preferred form, at least one peripheral edge lying perpendicular to a &lt;211&gt; crystallographic vector in the plane of one of the major surfaces. Thus, the crystal edges obtained are crystallographically offset 30.degree. as compared to those of Wey. Maskasky requires that the novel tabular grains be predominantly (that is, at least 50 mole percent) chloride.
Wilgus and Haefner U.S. Ser. No. 429,420, filed concurrently herewith and commonly assigned, titled HIGH ASPECT RATIO SILVER BROMOIODIDE EMULSIONS AND PROCESSES FOR THEIR PREPARATION, which is a continuation-in-part of U.S. Ser. No. 320,905, filed Nov. 12, 1981, now abandoned, discloses high aspect ratio silver bromoiodide emulsions and a process for their preparation.
Kofron et al U.S. Ser. No. 429,407, filed concurrently herewith and commonly assigned, titled SENSITIZED HIGH ASPECT RATIO SILVER HALIDE EMULSIONS AND PHOTOGRAPHIC ELEMENTS, which is a continuation-in-part of U.S. Ser. No. 320,904, filed Nov. 12, 1981, now abandoned, discloses chemically and spectrally sensitized high aspect ratio tabular grain silver halide emulsions and photographic elements incorporating these emulsions.
Daubendiek and Strong U.S. Ser. No. 429,587, filed concurrently herewith and commonly assigned, titled AN IMPROVED PROCESS FOR THE PREPARATION OF HIGH ASPECT RATIO SILVER BROMOIODIDE EMULSIONS, which is a continuation-in-part of U.S. Ser. No. 320,906, filed Nov. 12, 1981, now abandoned, discloses an improvement on the processes of Maternaghan whereby high aspect ratio tabular grain silver bromoiodide emulsions can be prepared.
Abbott and Jones U.S. Ser. No. 430,222, filed concurrently herewith and commonly assigned, titled RADIOGRAPHIC ELEMENTS EXHIBITING REDUCED CROSSOVER, which is a continuation-in-part of U.S. Ser. No. 320,907, filed Nov. 12, 1981, now abandoned, discloses the use of high aspect ratio tabular grain silver halide emulsions in radiographic elements coated on both major surfaces of a radiation transmitting support to control crossover.
Solberg, Piggin, and Wilgus U.S. Ser. No. 431,913, filed concurrently herewith and commonly assigned, titled RADIATION-SENSITIVE SILVER BROMOIODIDE EMULSIONS, PHOTOGRAPHIC ELEMENTS, AND PROCESSES FOR THEIR USE, which is a continuation-in-part of U.S. Ser. No. 320,909, filed Nov. 12, 1981, now abandoned, discloses high aspect ratio tabular grain silver bromoiodide emulsions wherein a higher concentration of iodide is present in an annular region than in a central region of the tabular grains.
Dickerson U.S. Ser. No. 430,574, filed concurrently herewith and commonly assigned, titled FOREHARDENED PHOTOGRAPHIC ELEMENTS AND PROCESSES FOR THEIR USE, which is a continuation-in-part of U.S. Ser. No. 320,910, filed Nov. 12, 1981, now abandoned, discloses producing silver images of high covering power by employing photographic elements containing forehardened high aspect ratio tabular grain silver halide emulsions.
Mignot U.S. Ser. No. 320,912, filed Nov. 12, 1981 and commonly assigned, titled SILVER BROMIDE EMULSIONS OF NARROW GRAIN SIZE DISTRIBUTION AND PROCESSES FOR THEIR PREPARATION discloses high aspect ratio tabular grain silver bromide emulsions wherein the tabular grains are square or rectangular in projected area.
Jones and Hill U.S. Ser. No. 430,092, filed concurrently herewith and commonly assigned, titled PHOTOGRAPHIC IMAGE TRANSFER FILM UNIT, which is a continuation-in-part of U.S. Ser. No. 320,911, filed Nov. 12, 1981, now abandoned, discloses image transfer film units containing tabular grain silver halide emulsions.
Evans et al U.S. Ser. No. 431,912, filed concurrently herewith and commonly assigned, titled DIRECT REVERSAL EMULSIONS AND PHOTOGRAPHIC ELEMENTS USEFUL IN IMAGE TRANSFER FILM UNITS which is a continuation-in-part of U.S. Ser. No. 320,891, filed Nov. 12, 1981, now abandoned, discloses image transfer film units containing tabular grain core-shell silver halide emulsions.